The present disclosure generally relates to slurries containing water, mineral particles, and a dispersant, as well as to methods for the preparation thereof.
Mineral fillers are relatively cheap substances which are, for example, added to materials, paints, paper, plastics, and the like, to increase the volume and/or weight but often also to improve the technical usability thereof. For example, calcium carbonate consists of naturally occurring materials and is often used in the pulp and paper industry. These naturally occurring minerals include, for example, limestone, marble, chalk, as well as shells of marine or coastal organisms, such as oyster shells.
Generally, mineral fillers have to be ground into particles to make them useful for the various possible applications. For example, calcium carbonate is generally prepared by first obtaining carbonate-containing raw materials by opencast or, underground quarrying. The quarried carbonate-containing raw materials together with inorganic or organic contaminations, which depend on the area of mining, are purified and then subjected to dry and/or wet processing. A preliminary comminution is performed by milling and, if necessary, subsequent flotation. Such starting materials are then subjected to further wet grinding at a solids content of 30-75% by weight using agitator-ball mills.
Milling can be done with or without media. In media milling, balls, pebbles or other media such as sand are used to grind the mineral particles to a desired particle size. Common methods of media milling are ball milling, attrition milling, sand milling, vertical and horizontal milling. In each case, media that are typically larger than the desired particle size to be ground are placed in a chamber, which is subsequently shaken, stirred, or otherwise agitated. By choosing the correct media material, particles can be milled down to average particle sizes of less than 1 micrometer.
Horizontal and vertical mills consist of circular containers oriented as labeled, in which disks or paddles, rotating at high speed impart intense impact and shear to comminute the mineral slurry particles. Horizontal mills incur higher installation costs and are more complex than vertical mills though horizontal mills are more energy efficient. Both mill types are energy intensive, however, and thus there exists a need for improved mineral grinding efficiency.
The major physical characteristics of mineral fillers for pulp and paper applications, for example, are median particle size, the distribution of particle size, brightness, and rheology in water at high solids. Unfortunately, higher solids content and increased particle fineness are properties which both increase the slurry viscosity. Current dispersants fail to provide stable slurries with high solids, low fines, and relatively low viscosity.
Accordingly, there exist needs for both improved grinding aids that increase milling efficiencies and for improved dispersants for mineral slurries.